Anti-blocking coated wrapper

ABSTRACT

AN ANTI-BLOCKING, WAX COATED, HEAT-SEALABLE WRAPPER WHICH IS PARTICULARLY SUITABLE FOR USE IN LONG TERM STORAGE OF CHEESE. THE WRAPPER HAS A CONVENTION FOIL OR THERMOPLASTIC SUBSTRATE UPON WHICH A MOISTURE PROOF LAYER OF WAX IS APPLIED. A PRIMING AGENT, SUCH AS TALC IS APPLIED   TO THE WAX LAYER AND A THIN WATER EMULSION COATING OF POLYVINYLIDENE CHLORIDE IS SUPER-IMPOSED ON THE PRIMED WAX LAYER.

y 1971 v. D'EYNCOURT STRICKLAND EI'AL 3,592,729

ANTI-BLOCKING COATED WRAPPER Filed March 11, 1968 PLASTIC PRIMER (TALC) WAX PLASTIC FILM/ METAL FOIL HTTP/(My;

United States Patent US. Cl. 161-220 16 Claims ABSTRACT OF THE DISCLOSURE An anti-blocking, wax coated, heat-sealable wrapper which is particularly suitable for use in long term storage of cheese. The wrapper has a conventional foil or thermoplastic substrate upon which a moisture proof layer of wax is applied. A priming agent, such as talc is applied to the wax layer and a thin water emulsion coating of polyvinylidene chloride is super-imposed on the primed Wax layer.

This invention relates to a coated wrapper and more particularly it relates to an anti-blocking. wax coated, heat sealable wrapper for food products.

Heat seal coatings of wax composition have advantages in packaging because of their low cost, low heat sealing temperatures, flexibility and moderately good impermeability to moisture vapour all of which are necessary for a satisfactory packaging medium. Their greater use has been prevented by poor slip for use on packaging machinery, poor mar resistance which is required to maintain the continuity of the coating and good appearance, poor grease and oil resistance, tendency to be alfected or damaged by the contents of the package, and poor oxygen gas impermeability which can cause rancidity of oily foodstuffs or cause spoilage by allowing the growth of mould in the contents.

In some applications improved grease and oil resistance, oxygen barrier properties and resistance to package contents may be obtained by prewrapping the contents with another packaging film, but this involves the extra expense of the packaging film and the extra cost of wrapping and if the film is first combined with the wrapper by applying it to the wax surface, heat seals at low temperature cannot be achieved.

Certain wax compositions used in the packaging of cheese, for example, have the added disadvantage that the wax composition is tacky so that it is impossible to separate individual sheets or unwind rolls of the wrappers unless an anti-blocking interleaving sheet is used or a non-blocking layer such as starch, talc or sorbic acid is applied to the wax surface. The anti-blocking interleaving sheet presents several problems such as bulky rolls or stacks of sheets, disposing of the material after it has fulfilled its function and the care that must be taken in winding up and slitting of rolls as in commercial practice blocking can still occur, especially in hot conditions. Starch is unacceptable in certain applications as an alternative to interleaving as the starch is a nutrient for mould and talc and sorbic acid, as well as starch, are objectionable as they may impair the heat scalability of the wax and cause a wrapper to have an undesirable powdery appearance.

As a further alternative, the wax coating may be covered with a thin sheet of plastic material, such as polyethylene. Such a coating is described in US. Pat. 3,075,864 to Anderson, issued J an. 29, 1963 and 3,010,860 to Eberl, issued Nov. 28, 1961. Anderson teaches that the polyethylene sheet is preformed and is adhered to ice the wax layer without fusion and Eberl teaches a polyethylene layer formed in situ on the wax layer with fusion between the wax and the polyethylene. Wrappers made by these methods are expensive and often heat sealing of the wax layers is not possible.

It is, therefore, an object of the present invention to provide a protective wrapper without the disadvantages previously described and which is easily heat sealed.

Another object of the present invention is to provide a method of coating a wax covered substrate with a thin protective film.

It has, surprisingly, been found that the objects of the present invention can be achieved by the application to the wax composition surface of an aqueous emulsion coating which forms a thin continuous film upon drying. Films formed from an emulsion coating are thinner than any commercial, preformed packing film which can be applied and are thin enough to permit satisfactory wax-like seals to be made.

It has further been found that a water based emulsion can be made to wet or otherwise achieve good flow over the wax surface and adhere firmly to said wax surface which is normally hydrophobic by first applying to the wax surface a dust or finely ground powder as a wetting or priming agent. Mica, starch or sorbic acid are among those material powders which may be used, and a particularly suitable material is talc powder U.S.P. because of its low cost, availability and inertness.

The novel features of our invention, together with the advantages thereof, may best be understood from the following description of specific embodiments when read in conjunction with the accompanying drawing in which numeral 1 designates a flexible sheet of substrate material, such as a plastic film or metal foil, numeral 2 designates a wax coating, such as a paraflin wax, numeral 3 designates a priming layer, such as talc or a lacquer and 4 designates a plastic aqueous emulsion coating such as polyvinylidene chloride.

Among the advantages of wrappers of the present invention is the fact that there is no possibility of residual taste or odour of organic chemical solvents which can affect the quality of flavour of a foodstuff which might be the contents of a package for which the wrapper is used. Other advantages are that the present wrappers can be made to have good slip, good mar resistance, good appearance, interleaving or powdering to prevent blocking is unnecessary, and the tendency to be damaged or affected by the contents of a package is eliminated.

The wrapper substrate may be any of the usual packaging materials which are capable of being coated with wax containing compositions by the usual industrial methods. Among these materials are plastic films, papers, metal foils and combinations thereof.

The wax containing coatings vary greatly in composition but generally contain more than about 30% paraffin or micro crystalline wax and are applied from a melt, without solvent or water. The other constituents of the wax composition may be selected from polyethylene, butyl rubber, rosin esters, ethylene copolymers and other commonly used wax composition materials either alone or in combination. The wax coating weights can vary from about 0.5 to about lbs. per 3000 sq. ft. and preferably about 10 lbs. to about 65 lbs. is employed.

As previously indicated,the wettability or priming of the wax containing surface is improved by dusting with powders such as talc, mica, starch or sorbic acid, but A other priming agents such as lacquers containing polymers of vinyl acetate, vinyl chloride or vinyl acetate copolymers such as those sold under the Trademark VMCH by Union Carbide and the Trademark GelvaV-l00 by Shawinigan Chemicals respectively can be used either alone or in combination with a powder. Other effective agents include polyacrylic latices and lacquers containing ethylene-vinyl acetate copolymers. The weight of powder used can vary widely bct typically between about A lb. to about lb. per 3000 sq. ft. is employed depending on the degree of adhesion and the specific agent employed. Similarly the weight of lacquer can vary widely between about /2 and 4 lbs. per 3000 sq. ft. and about 2 lbs. per 3000 sq. ft. is particularly suitable.

Although a wide range of plastic emulsion coatings can be used, it is preferable to use water emulsion coatings of polymers containing more than 40% vinyl acetate or vinylidene chloride (P. V. D. C.) in view of their low cost and, in the case of the latter, the excellent barrier properties to oils, moisture and gases. Polyvinyl acetate has superior adhesion to wax than P.V.D.C. and in some circumstances it may be preferable to apply to the wax a powder such as talc and then a layer of polyvinyl acetate followed by a layer of P.V.D.C. The coating weights can be varied depending upon the properties desired. Low weights such as 2 lbs. per 3000 sq. ft. allow the wax composition to activate most readily for heat sealing. High weights in the l-20 lb. range give the best slip, scuff resistance, and resistance to some contents of packages.

The wrappers of the present invention have many applications and one preferred application will now be described in detail in order to more fully illustrate the invention.

Flexible films and laminations are commonly used to wrap blocks of cheese and the flexible film or lamination is usually coated with a thick layer of wax composition so that after the cheese has been wrapped, the package can be sealed by the application of heat and pressure to the block of cheese so that the final package is impermeable to the passage of moisture vapour to prevent drying, and impermeable to the passage of oxygen gas which can cause mould growth. For example, a wrapper which is commonly used is made by laminating cellophane film to aluminum foil laminated to cellophane film plus a coating of wax composition on one surface. This combination has excellent moisture vapour and oxygen gas barrier properties making it very satisfactory for the packaging of blocks of cheese. Another example of a wrapper would be a lamination of cellophane to cellophane, omitting the aluminum foil, plus a coating of wax composition on one surface and this combination does not have such good moisture vapour and oxygen gas barrier properties compared to the first example because of the absence of the layer of aluminum foil which is impermeable, but the wrapper has the advantage that it is transparent so that the mould or other defects may be observed on the cheese without unwrapping the block.

In the case of packaging large blocks of natural cheddar cheese, for instance, 5 lb. to 40 lb. blocks, heat and pressure is commonly applied by a th Century Press. Sealing temperature of between about 160 F. and 210 F. are commonly used and achieved by the use of heated water circulating through the hollow walls of the press. Wax coating compositions which have the property of sealing at the temperature conditions used on the 20th Century Press and which are commonly used in cheese packaging wrappers are usually sticky mixtures of wax, resin and rubber which tend to block together making it impossible to separate individual sheets or unwind the rolls of the wrapper. Various methods have been employed to prevent this blocking effect, but as indicated above none are entirely satisfactory. We have found that a satisfactory wrapper is produced if a laminated sheet of cellophane film having a layer of wax composition amounting to 40 lb. per 3000 sq. ft. is dusted with a layer of fine powdered talc amounting to a weight of A to lb. per 3000 sq. ft. which is sufiicient to cover the surface of the wax to make it wettable by an emulsion. Lesser amounts do not adequately cover the surface of the Wax while greater amounts are unnecessary. Next a P.V.D.C. emulsion in water is applied to the tale coated Wax layer to give a coating weight of 3-10 lb. per 3000 sq. ft. after removal of the water by the drying tunnel. We have found that if the coating of P.V.D.C is applied by two or more independent passes, the effect is to produce a thin film which is continuous and with excellent barrier properties towards moisture vapour and oxygen gas. We have found that the P.V.D.C. emulsion Daran 220 (trademark) produced by Dewey & Almy Chemical Division of W. R. Grace and Co. is satisfactory for this purpose.

Satisfactory wrappers have been produced by the application of talc powder to the wax surface followed by the application of an aqueous emulsion of a polyvinyl acetate primer followed by the P.V.D.C. aqueous emulsion to form the protective film. This latter method resulted in improved adhesion of the P.V.D.C. film to the wax coating. Another application of the present invention is in the manufacture of bottle top membranes. Wax containing films are often used to seal bottle openings and are usually applied by pressure, with or without heat. Some goods, for example, hard candies, tend to mar or pick off the wax coating during shipping. If seals of the laminate of the present invention are employed, this disadvantage is overcome.

Overwraps are another application. In some cases in present commercial practice, an opaque porous paper tissue is applied over the clear wax containing surface and, on sealing, the coating penetrates through the tissue. This construction is opaque whereas wrappers of the present invention have the advantage of a transparent construction.

It will be appreciated from the foregoing that wrappers according to the present invention have many applications, and that Form-and-Fill packaging, where the web is partially formed into a package, filled and sealed is particularly appropriate. The wax composition gives body and flexibility at low cost to the construction and the emulsion coating the necessary degree of slip, mar resistance and inertness. If a relatively low weight emulsion coating is employed, conventional heat sealing means give strong seals to which the wax coating contributes.

If high emulsion coating weights are employed, and this is necessary in those cases where maximum inertness is required, special heat sealing equipment may be employed to ensure the higher heat sealing temperatures that may be required for good heat seals. Alternatively conventional heat sealing means may be used and a material with good heat sealing properties applied as an overall coating or pattern coating over the emulsion coating. The heat sealing coating may be applied from an emulsion or lacquer or as a melt.

We claim:

1. A low temperature heat scalable packaging material comprising consecutive layers of (a) a substrate layer which is a flexible sheet;

(b) a heat scalable mineral wax composition including at least 30% by weight of a paraffin wax or a microcrystalline wax;

(c) a primer coating which is a powder of talc, mica or starch; and

(d) an outer coating which is a continuous moisture resistant film that is the dried residue of an aqueous emulsion of a polymer.

2. The sheet material according to claim 1, wherein the powder coat is present in an amount from lb. to lb./3,000 sq. ft.

3. The sheet material according to claim 1, wherein said aqueous emulsion (d) is of a polyvinylidene chloride.

4. The sheet material according to claim 3, wherein said wax composition (b) is a wax-resin blend incorporating a resin selected from the group consisting of polyethylene, butyl rubber, rosin esters and ethylene copolymers.

5. The sheet material according to claim 3, wherein said wax composition (b) is present in an amount from lbs. to 65 lbs/3,000 sq. ft.

6. The sheet material according to claim 3, wherein said flexible sheet (a) is a polymer film, metal foil or paper.

7. The sheet material according to claim 3, wherein said flexible sheet (a) is a laminate of a polymer film and a metal foil.

8. The sheet material according to claim 3, wherein said flexible sheet (a) is cellophane or a cellophanealuminum foil laminate.

9. The sheet material according to claim 3, in the form of a wrapper.

10. A process for the production of a low temperature heat scalable sheet material for use in a package which comprises applying to a substrate layer which is a flexible sheet, a coat of a melt of a heat sealable mineral wax composition including at least 30% by weight of a paraffin wax or a microcrystalline wax and allowing said melt to solidify; applying to said coat a powder which is talc, mica or starch as an intermediate coat capable of forming a bond to a polymer; and applying to the thus coated wax composition a top coat of an aqueous emulsion of a polymer to form a continuous moisture resistant film and drying said top coat, said powder in said intermediate coat being applied only in an amount sufficient to effect bonding of said top coat to said wax composition coat.

11. The process according to claim 10, wherein the powder coating is applied in an amount from lb. to lb./3,000 sq. ft.

12. The process according to claim 10, wherein said polymer is a polyvinylidene chloride.

13. The process according to claim 12, wherein the wax composition is a blend of said mineral wax with a resin selected from the group consisting of polyethylene, butyl rubber, rosin esters and ethylene copolymers.

14. The process according to claim 12, wherein the coating of the wax composition is in an amount from 10 lbs. to lbs/3,000 sq. ft.

15. The process according to claim 12, wherein the flexible sheet is a polymer film, a metal foil or paper.

16. A process according to claim 12, wherein the flexible sheet is a laminate of a polymer film and a metal foil.

References Cited UNITED STATES PATENTS 2,341,885 2/1944 Sowa 117-26 3,196,038 7/1965 Schoch et a1. 117--76(P)X 3,276,899 10/1966 Mualberg et a1 11784X 3,355,348 11/1967 Lamar 1l776(P)X OTHER REFERENCES Du Pont, Polyvinyl acetate. Properties and applications of emulsions, solids, solutions.R and H Technical Bulletin, March 1641, 4 pages.

WILLIAM D. MARTIN, Primary Examiner R. HUSACK, Assistant Examiner U .5. Cl. X.R. 

